VMWare has published a whitepaper about LUN security in ESX. This is mainly in response to an article about potential security issues with ESX in a SAN environment. That article was quickly dismissed by people with knowledge about ESX.

ESX presents virtual SCSI devices to virtual machines. The virtual machines only see that virtual device. Even with raw device mappings, the virtual machine only sees the LUN that is assigned to it and cannot do anything else like scan for other LUNs on the SAN etc...

The whitepaper from VMWare also talks a little bit about N-Port ID virtualization (NPIV) which will provide a WWN-to-VM mapping. This allows storage admins to configure visibility of a SAN LUN to a virtual machine with their native toolset. Even with NPIV, virtual machines will only see the LUN that is assigned.